SPATIOTEMPORAL DYNAMICS OF LASERS WITH A LARGE FRESNEL NUMBER

We measure the local intensity and the intensity cross-correlation fun ction of patterns emitted by a CO2 laser with a Fresnel number around 60 and find evidence of weak turbulence. We show theoretically that th e spatiotemporal dynamics of such a laser can be governed by two field s. One leads to a ''turbulent'' state principally through phase fluctu ations, whereas the other yields a periodic modulation in space and ti me of the intensity. This can explain why the intensity of the laser i s locally chaotic but the time-averaged intensity pattern retains the global symmetry of the system.